1. Field of the Invention
The present invention relates to management of virtual concatenated channels and a transporting device for management of virtual concatenated channels where a signal is transmitted by distributing the signal in a plurality of channels in an SDH network.
2. Description of the Related Art
As high-speed data-transfer devices have been integrated into synchronous networks, an SDH (synchronous digital hierarchy) is now adopted as a global standard. A basic bit rate of the SDH is 155.52 Mbps, and a faster data transfer is available by using a multiple of the basic bit rate. A signal at the basic bit rate is referred to as synchronous-transport module 1 (STM-1). A signal transmitted at N times the basic bit rate is referred to as STM-N.
FIG. 1 is an illustrative drawing showing rules of multiplexing in the SDH.
FIG. 1 shows rules of multiplexing containers C-11 (1,544 kbps), C-12 (2,048 kbps), C-2 (6,312 kbps), C3 (44,736 kbps, 34,368 kbps), and C-4 (139,264 kbps) so as to become STM-N, which is N times the basic bit rate. These containers contain digital signals to be multiplexed.
In the figure, virtual containers VC-n (VC-11, VC-12, VC-2, VC-3, and VC-4) are comprised of a container and a path overhead attached thereto. A path overhead is used for error detection, network maintenance, etc. Tributary units TU-n (TU-11, TU-12, TU-2, TU-3, and TU-4) and administrative units AU-n (AU-3 and AU-4) are comprised of a virtual container and a pointer attached thereto for indicating a beginning of the virtual container. Further, tributary unit groups TUG-n (TUG-2 and TUG-3) are comprised of one or more tributary units.
FIG. 2 is an illustrative drawing showing a frame configuration of an STM-1 which has virtual containers VC-4 as a payload.
The STM-1 is comprised of 270 bytes by 9 rows. 9 bytes at the beginning together form a SOH (section overhead), and the following 261 bytes are the payload of the STM-1. The section overhead is used for maintenance and administration purposes to control section layers. A VC-4 includes therein a path overhead and the 149.76-Mbps payload thereof.
FIG. 3 is an illustrative drawing showing a configuration of the section overhead of the STM-1. The symbol xe2x80x9cxe2x88x92xe2x80x9d indicates a byte position that is currently unused. The section overhead is generated with respect to each transit transporting device. An AU pointer indicates a position of a beginning of a virtual container, which is included in the payload of STM-1.
FIG. 4 is a table showing a function assigned to each byte of the section overhead shown in FIG. 3. The present invention makes use of the unused portions of the section overhead, and has little to do with those portions which have established functions. A description of these functions, therefore, will be omitted.
As described above, the virtual containers have a path overhead attached thereto.
FIG. 5 is an illustrative drawing showing a path overhead of the virtual container VC-4.
A path overhead (VC-4POH) of the virtual container VC-4 is comprised of 1 byte by 9 rows
FIG. 6 is a table showing a function assigned to each byte of the path overhead.
As shown in the table, a J1 byte has a path-trace function, and a C2 byte has a function of indicating a signal type with regard to signals constituting the virtual container VC. In detail, the J1 byte includes information stored therein regarding a path. A network administrator has a latitude to some extent in writing the contents of the J1 byte, with a requirement that a 16-byte message be used based on a multi-frame configuration. The C2 byte indicates signal types with regard to signals constituting the virtual containers to be multiplexed. By referring to the virtual container VC, it is possible to check whether the virtual container is EQUIP or UNEQ. This serves as an EQUIP/UNEQ signal of the virtual container VC.
According to the standard, the path overhead of the virtual container VC-2 is different from the path overhead of the virtual container VC-4. Since no significant difference exists in the basic functions, however, the path overhead of the virtual container VC-2 can be interpreted and understood in the same manner as interpreting the pass overhead of the virtual container VC-4.
FIG. 7 is an illustrative drawing showing a case in which a video signal of 34 Mbps is transmitted as an SDH signal in an SDH network.
When the video signal is transmitted by using virtual containers VC-2, the signal is first converted into an SDH signal by a transporting device #1, and is sent via transporting devices #2 and #4 to a transporting device #3, where the signal is converted back to the original video signal. The video signal thus obtained is output from the transporting device #3.
FIG. 8 is a block diagram of a related-art transporting device.
A video signal, which is multiplexed in synchronism with 34-MHz frames, has a frame synchronization established by a frame-synchronization circuit 2, and, then, is extracted by a video-signalextraction circuit 3. The extracted video signal is divided into an audio signal and video images IMAGE1 through IMAGE4 based on frequency bands thereof by a dividing circuit 4. The audio signal and video images are subjected to mapping by VC-2 mapping circuits 5 through 9, respectively, and have a path overhead (VC-2POH) attached thereto by VC-2POH-insertion circuits 10 through 14, respectively. This creates virtual containers VC-2. A multiplexing circuit 15 multiplexes the virtual containers VC-2 and another virtual container VC-12. The multiplexed signal is then provided with a section overhead (STM-1SOH) by an STM-1SOH-insertion circuit 16, resulting in an STM-1.
In a related-art transmission scheme, when a large amount of data is distributed to a plurality of channels, each divided chunk of data needs to be transmitted via the same network route in order to reconstruct the original data readily on the receiver side.
In FIG. 7, for example, a single video signal is divided into 5 virtual containers VC-2. If the 5 virtual containers VC-2 travel the same route to reach the transporting device #3, there is no problem in reconstructing the video signal. However, if some of the 5 virtual containers VC-2 travel through the transporting device #4 and others travel through the transporting device #2, the video signal reaching the transporting device #3 will have a different arrival time and a different signal level, depending on the route it takes. As a result, the transporting device #3 needs to attend to timing adjustment as well as level adjustment in order to compensate for route differences.
In order to obviate this problem, route settings need to be made so as to insure that chunks of data distributed to a plurality of channels are transmitted through the same network route. There is no method known in the field, however, to check such route settings easily as to whether they are correctly set.
Accordingly, there is a need for a scheme which makes it possible to easily check whether route settings are correctly made in a virtual concatenated transmission when data is distributed to a plurality of channels in an SDH network.
Accordingly, it is a general object of the present invention to provide a scheme which satisfy the need described above.
It is another and more specific object of the present invention to provide a method and a device which make it possible to easily check whether route settings are correctly made in a virtual concatenated transmission when data is distributed to a plurality of channels in an SDH network.
In order to achieve the above object according to the present invention, a method of controlling virtually concatenated channels includes the steps of a) distributing a signal to a plurality of channels in an SDH network so as to transmit the signal, and b) providing information at a predetermined position within each one of the channels or at predetermined positions within multi-frames containing an entirety of the channels, the information indicating whether a corresponding one of the channels is concatenated.
In the method described above, concatenation information on a given channel is provided at a predetermined position in the given channel or at a predetermined position in multi-frames. Because of this arrangement, a transporting device which receives the signal can compare the concatenation information with the current communication-line settings, and detects an error in the communication-line settings when there is a mismatch. This enables a transporting device to check whether all the channels are being transmitted via the same route as required by the line settings. Further, a check can be made at each transporting device as to whether there is an error in the line settings.
According to another aspect of the present invention, the method as described above is such that the step b) provides the information at a path trace of a path overhead of each channel.
In the method described above, a path overhead, which is defined by a standard, is utilized so as to carry the concatenation information. This makes it possible to detect a line-setting error as easily as in the previously described method while staying within the boundary of the standard.
According to another aspect of the present invention, the method as described above is such that the step b) provides the information at an unused portion of a path overhead of each channel.
In the method described above, a path overhead, which is defined by a standard, is utilized so as to carry the concatenation information. This makes it possible to detect a line-setting error as easily as in the previously described method while staying within the boundary of the standard.
According to another aspect of the present invention, the method as described above is such that the step b) provides the information at an unused portion of a section overhead of multi-frames containing the entirety of the channels.
In the method described above, a section overhead, which is defined by a standard, is utilized so as to carry the concatenation information. This makes it possible to detect a line-setting error as easily as in the previously described method while staying within the boundary of the standard.
According to another aspect of the present invention, the method as described above further includes the steps of receiving at a receiver the signal distributed to the plurality of channels, comparing the information included in the received signal with EQIP/UNEQ signals included in path overheads of the plurality of channels, and signaling an alarm if the comparison finds a mismatch.
In the method described above, an error in the concatenation information is easily detected by checking a consistency between the concatenation information included in the section overhead and the EQIP/UNEQ signals included in the path overheads and by signaling an alarm if there is inconsistency.
According to another aspect of the present invention, the method as described above further includes the steps of receiving at a receiver the signal distributed to the plurality of channels, comparing the information included in the received signal with communication-line settings, and signaling an alarm if the comparison finds a mismatch.
In the method described above, an error in the communication-line settings is easily found by comparing the information included in the received signal with the communication-line settings and by signaling an alarm if the comparison finds a mismatch. This also serves to find an line-setting error at each transporting device.
According to another aspect of the present invention, the method as described above is such that the signal is a 34-Mbps video signal, and the plurality of channels are VC-2 virtual containers, the multi-frames including STM-1 frames.
In the method as described above, only five virtual containers VC-2 are necessary whereas seven virtual containers VC-3 would be needed if the 34-Mbps signal were to be included in VC-3 virtual containers.
According to another aspect of the present invention, a device for controlling virtually concatenated channels includes distributing means for distributing a signal to a plurality of channels in an SDH network so as to transmit the signal, and information providing means for providing information at a predetermined position within each one of the channels or at predetermined positions within multi-frames containing an entirety of the channels, the information indicating whether a corresponding one of the channels is concatenated.
According to another aspect of the present invention, the device as described above is such that the information providing means provides the information at a path trace of a path overhead of each channel.
According to another aspect of the present invention, the device as described above is such that the information providing means provides the information at an unused portion of a path overhead of each channel.
According to another aspect of the present invention, the device as described above is such that the information providing means provides the information at an unused portion of a section overhead of multi-frames containing the entirety of the channels.
According to another aspect of the present invention, a device for controlling virtually concatenated channels in an SDH network includes dividing circuit which divides a signal to a plurality of channels, a first overhead-generation circuit which attaches a first overhead to each of the channels, the first overhead includes information indicating whether a corresponding one of the channels is concatenated, multiplexing circuit which multiplexes the plurality of channels with the first overhead attached thereto to generate a frame, and a second overhead-generation circuit which attaches a second overhead to the frame.
According to another aspect of the present invention, a device for controlling virtually concatenated channels in an SDH network includes dividing circuit which divides a signal to a plurality of channels, a first overhead-generation circuit which attaches a first overhead to each of the channels, multiplexing circuit which multiplexes the plurality of channels with the first overhead attached thereto to generate multi-frames, and a second overhead-generation circuit which attaches second overheads to the multi-frames, the second overheads includes information indicating whether a corresponding one of the channels is concatenated.
According to another aspect of the present invention, a device for checking communication-line settings in an SDH network includes a concatenation-information detection circuit which obtains concatenation information from a signal that is received, the signal being distributed to a plurality of channels prior to receipt thereof and including the concatenation information provided at a predetermined position within each one of the channels or at predetermined positions within multi-frames containing an entirety of the channels, the information indicating whether a corresponding one of the channels is concatenated, a communication-line setting resister which stores current communication-line settings, and a matching circuit which compares the concatenation information with the current communication-line settings, and signals an alarm when the comparison finds a mismatch.
The devices described above are so configured as to practice a corresponding one of the methods previously described.